Broadcast Urea Research Articles

Rescue Nitrogen Applications for Corn

Rescue N applications to corn (Zea mays L) may be needed when wet conditions prevent N applications or when the loss of applied N is suspected due to wet conditions. Crop injury when N is broadcast applied may counteract the yield benefits of a rescue N application. The objective of this research was to determine the effect of corn height, N placement, and source on injury and yield response. Five site‐years of research evaluated the impact of broadcast and between‐row placement of NH4NO3 (AN), urea–NH4NO3 (UAN), urea, and urea plus N‐(n‐butyl) thiophosphoric triamide (NBPT), a urease inhibitor, at 170 kg N ha−1 either preplant or when the corn was 30, 60, 90, or 120 cm tall. Visual injury for broadcast‐applied N sources was ranked urea = urea plus NBPT < AN ≤ UAN 7 d after treatment. Injury was dependent on plant height. Leaf injury resulted in reduced yield when UAN or AN was broadcast on corn that was 60, 90, or 120 cm tall. Broadcast urea or urea plus NBPT caused minimal crop injury and effectively supplied N to the corn crop. Application of NBPT‐treated urea increased yield 260 kg ha−1 averaged across timings when compared with urea alone. Application when corn was 30 cm tall produced the highest yields, but excellent yield response to rescue N was obtained at all application heights. The placement and source of N should be considered when rescue N applications are made to corn >30 cm tall.

Lâminas de irrigação e doses de nitrogênio em pastagem de capim-elefante no período seco do ano no norte de Minas Gerais

Neste trabalho avaliou-se durante o período seco do ano o efeito de quatro doses de nitrogênio (100, 300, 500 e 700 kg.ha-1.ano) e de seis lâminas d'água (0, 20, 40, 80, 100 e 120% da evapotranspiração de referência) sobre o rendimento forrageiro, a densidade de perfilhos, a relação folha/colmo, a altura de plantas e os teores de proteína bruta e fibra em detergente neutro do capim-elefante (Pennisetum purpureum, Schum). O delineamento experimental foi o de blocos casualizados com quatro repetições. Como fonte de adubo nitrogenado utilizou-se ureia, aplicada a lanço. O controle do nível de água e a definição do momento de irrigar foram estabelecidos com base na curva de retenção de água no solo e no teor de água, pelo método gravimétrico de amostras de solo. As lâminas d'água e as doses de nitrogênio aumentaram linearmente a altura das plantas, a produção de matéria seca e a densidade de perfilhos, mas diminuíram os teores de PB. A irrigação teve efeito quadrático no teor FDN, cujo percentual máximo, 69,38%, foi observado quando foi aplicada lâmina d'água de 72,88% da evapotranspiração. A adubação nitrogenada reduziu linearmente o teor de FDN. A menor relação folha/colmo obtida foi de 1,98 quando aplicada lâmina d'água de 65,5% da evapotranspiração com a dose de 300 kg.ha-1.ano de nitrogênio. As lâminas d'água associadas às doses de nitrogênio elevam a produção de MS de 2.539,08 kg/corte para 6.445,72 kg/corte, diminuindo o efeito da estacionalidade de produção do capim-elefante "pioneiro" no norte de Minas Gerais.

Banding of Urea Increased Ammonia Volatilization in a Dry Acidic Soil

Volatilization of ammonia following application of urea contributes to smog formation and degradation of natural ecosystems. The objective of this study was to evaluate the impact of (i) incorporation and banding of urea and (ii) surface broadcast of slow-release urea types on NH(3) volatilization in a dry acidic soil. Volatilization was measured using wind tunnels for 25 d after standard urea (140 kg N ha(-1)) was broadcast, broadcast and incorporated (0-5 cm), or incorporated in shallow bands (3-5 cm) to a conventionally tilled silty loam soil. Urea supplemented with a urease inhibitor or coated with a polymer was also broadcast at the soil surface. Little N diffused out of the polymer-coated granules and ammonia losses were low (4% of applied N). Use of a urease inhibitor also resulted in a low NH(3) loss (5% of applied N) while maintaining soil mineral N at levels similar to plots where untreated urea was broadcast. The rate of hydrolysis of urea broadcast at the soil surface was slowed by the lack of moisture and NH(3) loss (9% applied N) was the lowest of all treatments with standard urea. Incorporation of broadcast urea increased emissions (16% applied N) by increasing urea hydrolysis relative to surface application. Furthermore, incorporation in band also increased emissions (27% applied N) due to a localized increase in soil pH from 6.0 to 8.7. We conclude that incorporating urea in bands in a dry acidic soil can increase NH(3) volatilization compared to broadcast application followed by incorporation.

Ammonia volatilization following surface application of urea to tilled and no-till soils: A laboratory comparison

Broadcasting of urea to agricultural soils can result in considerable losses by NH 3 volatilization. However, it is unclear if the impact of this practice on NH 3 emissions is further enhanced when performed on no-till (NT) soils. The objective of this study was to compare NH 3 volatilization following broadcasting of urea to NT and moldboard plowed (MP) soils. Intact soil cores were taken shortly after harvest from NT and MP plots of three long-term tillage experiments in Québec (Canada) and stored for 4.5 months prior to incubation. Urea (14 g N m −2) was applied at the soil surface and NH 3 volatilization was measured for 30 d using an open incubation system. Mean cumulative NH 3 losses were greater ( P < 0.001) in NT (3.00 g N m −2) than in MP (0.52 g N m −2). Several factors may have contributed to the higher emissions from the NT soils. Urease activity in the top 1 cm of soils was on average 4.2 times higher in NT than in MP soils. As a result, hydrolysis of urea occurred very rapidly in NT soils as indicated by enhanced NH 3 emissions 4 h after application of urea. The presence of crop residues at the surface of NT soils also decreased contact of the urea granules with the soil, possibly reducing adsorption of NH 4 + on soil particles. Lower volatilization on the MP soils may also have partly resulted from a fraction of urea granules falling into shallow cracks. Field trials are needed to confirm our finding that NT soils bear greater potential for NH 3 volatilization following surface application of urea than MP soils.

Reducing ammonia volatilization in a no-till soil by incorporating urea and pig slurry in shallow bands

Incorporation of broadcast pig slurry and urea into soil is incompatible with no-till production systems and alternative application methods that reduce NH3-N loss are required. The objective of this study was to assess the impact of incorporating urea and pig slurry in shallow furrows (banding) on NH3 volatilization. A field study was conducted on a silty loam soil that had been under no-till for 2 years. Ammonia volatilization was measured for 29 days after urea and pig slurry (140 kg N ha−1) were broadcast or incorporated (5 cm) in bands. High urease activity and soil temperatures as well as an absence of rainfall combined to result in large losses of NH3-N from all treatments. Broadcast urea lost the greatest proportion of applied N (64%) followed by banded urea (31%), broadcast pig slurry (29%) and banded pig slurry (16%). High emissions from broadcast urea were consistent with previous reports of large volatilization losses on no-till soils. Presence of crop residues and associated high urease activity (288 μg NH4-N g−1 h−1) at the surface of no-till soils were likely important factors contributing to these high emissions. Incorporation of slurry and urea in bands was not as efficient in reducing volatilization as expected but not for the same reason. Relatively high emissions from banded slurry were the result of an incomplete incorporation of slurry in the shallow bands and indicate that the benefit of this practice is limited at high slurry application rates. In banded urea plots, hydrolysis of concentrated urea likely resulted in high localized NH4+ concentrations and pH, which increased NH3 source strength and emissions. Our results therefore suggest that incorporating urea in bands may not be as efficient for reducing NH3 emissions as incorporation of broadcasted urea which results in lower soil urea concentrations.

Ammonia exchange between rice leaf blades and the atmosphere: Effect of broadcast urea and changes in xylem sap and leaf apoplastic ammonium concentrations

To elucidate the effects of broadcast urea on ammonia (NH3) exchange between the atmosphere and rice, we investigated the NH3 exchange flux between rice leaf blades and the atmosphere, xylem sap ammonium (NH+ 4) concentration, leaf apoplastic NH+ 4 concentration and pH, and determined the stomatal NH3 compensation point. Paddy rice (Oryza sativa L. cv. Nipponbare) cultivation using experimental pots was conducted in the open air. Three treatments, no nitrogen (NN), standard nitrogen (SN) and high nitrogen (HN), were prepared for two supplemental fertilizations. Urea with 0, 30 and 60 kg N ha−1 for the NN, SN and HN treatments, respectively, was broadcast at panicle initiation, and urea with 0, 20 and 40 kg N ha−1 for the NN, SN and HN treatments, respectively, was broadcast at heading. The NH3 exchange fluxes between the rice leaf blades and the atmosphere (SN treatment) measured using a dynamic chamber technique showed net deposition in general; however, net emission from the old leaves occurred 1 day after the application at heading. In contrast, the xylem sap NH+ 4 concentrations increased markedly 1 day after both applications, which suggests direct transportation of NH+ 4 from the rice roots to the above-ground parts. The applications resulted in no obvious increase in the leaf apoplastic NH+ 4 concentrations. The relationship between the NH+ 4 concentration in the xylem sap and that in the leaf apoplast was uncertain, although the NH+ 4 in the xylem sap came from the roots and the NH+ 4 in the apoplast might be affected by the stomatal deposition of NH3. The stomatal NH3 compensation point of rice was estimated to be 0.1–4.1 nmol mol−1 air (20°C). The direction and intensity of the exchange flux through the stomata, interpreted on the basis of the temperature-corrected NH3 compensation point, agreed with the observed exchange flux between the rice leaf blades and the atmosphere.

Fertilizer N management and P placement effects on yield, seed protein content and N uptake of flax under varied conditions in Saskatchewan

In the Canadian prairies, producers prefer to seed and apply all fertilizer nutrients in one operation, but placement of fertilizers at high rates in the seed row can reduce crop emergence. Recently, specialized equipment has been developed to minimize or prevent damage to seedlings by maintaining a safe separation between seed and fertilizer. A 3-yr (2000 to 2002) field study was conducted to determine the effect of N formulation (urea and anhydrous ammonia), placement (broadcast, side-band and mid-row band), timing (fall and spring) and rate (0 to 90 or 120 kg N ha-1), and P placement (7–10 kg P ha-1) on plant density, seed and straw yield, seed protein content, and N uptake in seed and straw of flax (Linum ustatissimum L.) under no-till at four sites (Indian Head, Black Chernozem soil – Udic Boroll; Melfort, Dark Gray Luvisol soil – Mollic Cryoboralf; Swift Current, Brown Chernozem soil – Aridic Boroll; and Scott, Dark Brown Chernozem soil – Typic Boroll) in Saskatchewan. There was a significant increase at 10 of 12 site-years for seed yield, at 5 site-years for straw yield, at 12 site-years for seed protein content, at 11 site-years for seed N uptake, and at 8 site-years for straw N uptake with increasing N fertilizer rate, but the responses were generally small to moderate and varied with placement, form and timing of N application, and placement of P fertilizer in a few cases. Side-banded N fertilizer treatments reduced plant emergence at 3 site-years for urea and at 4 site-year for anhydrous ammonia, but the plant densities were considered adequate for optimum yield. Seed and straw yield, seed protein content, and N uptake in seed and straw were generally similar between side-banded and mid-row-banded N fertilizer, and also similar between urea and anhydrous ammonia in most cases.Occasionally, there was a trend of seed yield reduction with seed-placed P compared with side-banded P, side-banded urea was more effective than broadcast urea, and fall banded N less effective than spring side-banded N. In conclusion, there were few differences in the agronomic performance of urea vs. anhydrous ammonia and side-band vs. mid-row band. The findings did suggest that broadcast urea can be less effective than side-banded urea, fall banded N can be inferior to spring banded N, and seed-placed P can reduce seed yield compared with side-banded P. Key words: Anhydrous ammonia, flax, N application timing, N form, N and P placement, N uptake, protein content, urea, yield

Temporal and Spatial Variations in N2O Emissions from a Chinese Cabbage Field as a Function of Type of Fertilizer and Application

We conducted a field experiment in an Andosol near Tsukuba (Japan) to study the effects of the type of nitrogen fertilizer on nitrous oxide (N2O) emissions and on nitrogen uptake by Chinese cabbage (Brassica campestris L.). We used four treatments: fertilizer containing no nitrogen (CONT), broadcast application of urea (BR-U), band application of urea (B-U), and band application of controlled-release urea (B-CU). The application rate was 250 kg N ha−1, a conventional rate in the region. We measured N2O flux two or three times a week during the 82-day growth period, then divided the cumulative emissions into three stages: early (28 days), middle (27 days), and late (27 days). The temporal variation in N2O emissions differed among the treatments. Broadcast urea application produced 70% of N2O emissions during the early stage. N2O emissions increased with increasing cabbage growth in the CONT treatment, indicating that plant growth accompanied by increasing root biomass could stimulate N2O emissions from unfertilized soil. There were no differences in the patterns of temporal variation in N2O flux between the two band applications (B-U and B-CU); N2O emissions in the early and middle stages were 46 and 42%, respectively, for B-U, vs. 41 and 40% for B-CU. However, the overall N2O emission was reduced by 40.5% in the B-CU treatment compared with the B-U treatment. N2O emissions from the soils within fertilized bands were dramatically higher than those between the fertilized bands, and this trend continued until harvesting.

Nitrogen Oxide and Methane Emissions under Varying Tillage and Fertilizer Management

Comprehensive assessment of the total greenhouse gas (GHG) budget of reduced tillage agricultural systems must consider emissions of nitrous oxide (N2O) and methane (CH4), each of which have higher global warming potentials than carbon dioxide (CO2). Tillage intensity may also impact nitric oxide (NO) emissions, which can have various environmental and agronomic impacts. In 2003 and 2004, we used chambers to measure N2O, CH4, and NO fluxes from plots that had been managed under differing tillage intensity since 1991. The effect of tillage on non-CO2 GHG emissions varied, in both magnitude and direction, depending on fertilizer practices. Emissions of N2O following broadcast urea (BU) application were higher under no till (NT) and conservation tillage (CsT) compared to conventional tillage (CT). In contrast, following anhydrous ammonia (AA) injection, N2O emissions were higher under CT and CsT compared to NT. Emissions following surface urea ammonium nitrate (UAN) application did not vary with tillage. Total growing season non-CO2 GHG emissions were equivalent to CO2 emissions of 0.15 to 1.9 Mg CO2 ha(-1) yr(-1) or 0.04 to 0.53 Mg soil-C ha(-1) yr(-1). Emissions of N2O from AA-amended plots were two to four times greater than UAN- and BU-amended plots. Total NO + N2O losses in the UAN treatment were approximately 50% lower than AA and BU. This study demonstrates that N2O emissions can represent a substantial component of the total GHG budget of reduced tillage systems, and that interactions between fertilizer and tillage practices can be important in controlling non-CO2 GHG emissions.

Nitrogen Application to Soybean at Early Reproductive Development

Nitrogen application during soybean [Glycine max (L.) Merrill] reproductive stages has the potential to increase soybean productivity. The objective of this study was to determine the impact of N fertilizer applied to the soil at the beginning pod growth stage on soybean yield and grain quality. Additional objectives were to study alternative N fertilizer and application practices that might enhance soybean use of applied N. A field study was conducted at five locations in Iowa during 1999 and 2000. Nitrogen treatments were urea and polymer‐coated urea broadcast and subsurface band placed between the rows at 45 and 90 kg N ha−1 and a no‐N control. The study showed few, small, and inconsistent effects of N material, placement, and rate on grain yield and quality components at individual sites or when combined across individual sites. There were no significant effects on grain yield, with only a 39 kg ha−1 increase from applied N. Grain protein, oil, and fiber concentrations were the same with or without N application. Aboveground plant dry matter (DM) at the R6 growth stage was greater with the higher N rate, but plant DM with N application was lower than the no‐N control. Nitrogen concentration in plant DM was significantly increased with applied N. In conclusion, N application increased N concentration in R6 soybean plants, but N rate and alternative application practices had no positive effect on plant DM, grain N concentration and removal, grain yield, or grain quality components. It was concluded that growers should not consider fertilizer N applied to soil during early reproductive stages as a method to increase soybean yield or grain quality.

Ammonia Volatilization Loss from Surface-Broadcast Urea: Comparison of Vented- and Closed-Chamber Methods and Loss in Winter Wheat–Summer Maize Rotation in North China Plain

Ammonia (NH3) volatilization is an important pathway for fertilizer nitrogen (N) loss from soil and is also a major source of air and environmental pollution. On calcareous soils in North China Plain, application of N fertilizer in the form of urea under intensive cropping with winter wheat (Triticum aestvum L.) and summer maize (Zea mays L.) rotation can lead to serious NH3 loss. The objective of this study was to compare a modified vented-chamber method with the traditional closed-chamber method to measure NH3 volatilization loss under laboratory and field conditions and to determine in situ NH3 volatilization in the field from surface broadcast urea at 0, 120, 240, and 360 kg N ha−1 rates to each crop (for winter wheat, one-half at sowing and the other half at the elongation growth stage; for summer maize, one-half at the 3-leaf and the other half at the 10-leaf growth stage) in a winter wheat and summer maize rotation at the northern edge of North China Plain from October 1998 to September 1999. Urea was surface applied after irrigation before sowing, or prior to irrigation during the growing season. Compared to the closed chamber method, the vented chamber method was found to be simpler in structure, easier to operate, more suitable for in situ determination of NH3 volatilization in the field, and had higher recovery of emitted NH3 (99.5 vs. 70.8%). For surface broadcast urea after first irrigation prior to sowing of winter wheat, the NH3 volatilization rate reached, a maximum on the second to fifth day after application. Total NH3 loss from soil during the October 8 to November 18, 1998, period was 2.9, 4.8, 10.5, and 35.7 kg N ha−1 at the 0, 60, 120, and 180 kg N ha−1 rates, respectively. When urea was top-dressed prior to irrigation at the elongation growth stage of the winter wheat in midspring, NH3 loss was relatively low (i.e., 1.5, 2.1, 2.4, and 2.7 kg N ha−1 at 0, 60, 120, and 180 kg N ha−1 rates, respectively). The NH3 loss from urea for the entire winter wheat–growing season accounted for 2.1, 3.6, and 9.5% of the applied N at 120, 240, and 360 kg N ha−1 rates, respectively. For summer maize where urea was top-dressed at the 3-leaf and 10-leaf growth stages, the NH3 volatilization rate increased more quickly and maximized on the first or second day after N application. During the summer maize–growing season, total NH3 loss from urea accounted for 5.6, 4.8, and 4.9% of the applied N at 120, 240, and 360 kg N ha−1 rates, respectively. Based on the results of this study, total NH3 loss was estimated to range from 163,000 to 477, 200 Mg of N from soil in a winter wheat–summer maize rotation in North China Plain. Of these, about 68,400 to 382,600 Mg of N loss were from the N fertilizer surface applied as urea.

Effect of crop residue management on nitrogen dynamics and balance in a lowland rice cropping system

Two field experiments were conducted in a rice–fallow–rice cropping sequence during consecutive dry and wet seasons of 1997 on a Fluvic Tropaquept to determine the fate and efficiency of broadcast urea in combination with three residue management practices (no residue, burned residue and untreated rice crop residue). Ammonia volatilization losses from urea (70 kg N ha−1) broadcast into floodwater shortly after transplanting for 11 d were 7, 12 and 8% of the applied N from no residue, burned residue and residue treated plots, respectively. During that time, the cumulative percent of N2 + N2O emission due to urea addition corresponded to 10, 4.3 and nil, respectively. The 15N balance study showed that at maturity of the dry season crop, fertilizer N recovery by the grain was low, only 9 to 11% of the N applied. Fifty to 53% of the applied 15N remained in the soil after rice harvest, mainly in the upper 0–5 cm layer. The unaccounted for 15N ranged from 27 to 33% of the applied N and was unaffected by residue treatments. Only 4 to 5% of the initial 15N-labeled urea applied to the dry season rice crop was taken up by the succeeding rice crop, to which no additional N fertilizer was applied. Grain yield and N uptake were significantly increased (P=0.05) by N application in the dry season, but not significantly affected by residue treatments in either season.

Impact of organic residue management on nitrogen use efficiency in an annual rice cropping sequence of lowland Central Thailand

Field experiments were conducted in Central Thailand under a rice–fallow–rice cropping sequence during consecutive dry and wet seasons of 1998 to determine the impact of residue management on fertilizer nitrogen (N) use. Treatments consisted of a combination of broadcast urea (70 kg N ha−1) with rice straw (C/N 67) and rice hull ash (C/N 76), which were incorporated into the puddled soil 1 week before transplanting at a rate of 5 Mg ha−1. Nitrogen-15 balance data showed that the dry season rice recovered 10 to 20% of fertilizer N at maturity. Of the applied N, 27 to 36% remained in the soil. Loss of N (unaccounted for) from the soil–plant system ranged from 47 to 54% of applied N. The availability of the residue fertilizer N to a subsequent rice crop was only less than 3% of the initial applied N. During both season fallows NO3-N remained the dominant form of mineral-N (NO3+NH4) in the aerobic soil. In the dry season grain yield response to N application was significant (P=0.05). Organic material sources did not significantly change grain yield and N accumulation in rice. In terms of grain yields and N uptake at maturity, there was no significant residual effect of fertilizer N on the subsequent rice crop. The combined use of organic residues with urea did not improve N use efficiency, reduced N losses nor produced higher yields compared to urea alone. These results suggested that mechanisms such as N loss through gaseous N emissions may account for the low fertilizer N use efficiency from this rice cropping system. Splitting fertilizer N application should be considered on the fertilizer N use from the organic residue amendment.

Effect of rice straw management on nitrogen balance and residual effect of urea-N in an annual lowland rice cropping sequence

Two field experiments were conducted in 1999 (wet season) and 2000 (dry season) on a Ustic Endoaquerts in central Thailand to examine the impact of rice straw management practices on rice yield, N uptake and fertilizer-N use efficiency. Treatments included a combination of urea broadcast at a rate of 70 kg N ha−1 with either straw or compost which were incorporated at a rate of 5 Mg ha−1. At maturity of the wet season rice, 15N recovery by the grain was low (11–14%) as well as straw-N derived from labeled N (5–7%). After harvest, 25–29% of applied N still remained in the soil, mainly in the 0 to 5-cm layer. Large amounts of fertilizer-N (53–55%) were lost (unaccounted for) from the soil/plant system during the first crop. Residual fertilizer-N recovery in the second rice crop was less than 3% from the original application. During both fallow seasons NO3−-N remained the dominant form of mineral N (NO3− + NH4+) in the soil but its concentration was low. In the wet season grain yield response to N application was significant (P =0.05). Organic material sources did not significantly change grain yield and N accumulation in rice. In terms of grain yield and N uptake at maturity, there was no significant residual effect of fertilizer-N on the subsequent rice crop. These results indicated that the combined use of organic residues with urea did not decrease total N losses or increase crop yield or uptake of N compared to urea alone.

N2O and NO emissions from a field of Chinese cabbage as influenced by band application of urea or controlled-release urea fertilizers

A field experiment was conducted in an Andosol in Tsukuba, Japan to study the effect of banded fertilizer applications or reduced rate of fertilizer N (20% less) on emissions of nitrous oxide (N2O) and nitric oxide (NO), and also crop yields of Chinese cabbage during the growing season in 2000. Six treatments were applied by randomized design with three replications, which were; no N fertilizer (CK); broadcast application of urea (BC); band application of urea (B); band application of urea at a rate 20% lower than B (BL); band application of controlled-release urea (CB) and band application of controlled-release urea at a rate 20% lower than CB (CBL). The results showed that reduced application rates, applied in bands, of both urea (BL) and controlled-release urea fertilizer (CBL) produced yields that were not significantly lower than yields from the full rate of broadcast urea (BC). The emissions of N2O and NO from the reduced fertilizer treatments (BL, CBL) were lower than that of normal fertilizer rates (B, CB). N2O and NO emissions from controlled-release urea applied in band mode (CB, CBL) were less than those from urea applied in band mode (B, BL). The total emissions of N2O and NO indicated that applying fertilizers in band mode mitigated NO emission from soils, but N2O emissions from banded urea (B) were no lower than from broadcast urea (BC).

Management of rhizoctonia bare patch in the South Australian mallee using a modified direct drilling system, deep-banded urea, and sowing time in relation to the break in the season

Tillage experiments in the South Australian mallee, over 8 years (1990–97), have demonstrated that cultivation directly below the seed at sowing controls rhizoctonia bare patch as effectively as 1 or 2 cultivations prior to sowing. When combined with a short chemical fallow and the use of press-wheels, this modified direct drilling technique can yield as well as, or better than, conventional farming systems. The combination of modified direct drilling and deep-banded urea increases the control of the disease in the first 2 weeks after the break in the season. In the first 2 weeks after the break, deep banding urea at sowing is more likely to increase yield, than modified direct drilling with urea broadcast at tillering, when both treatments are compared with standard direct drilling. In a reduced tillage system, a cultivation 6–11 days after the break in the season may be more effective in reducing bare patch than a cultivation at other times after the break.

Urea Placement and Nitrification Inhibitor Effects on Growth and Nitrogen Accumulation by No‐Till Winter Wheat

Reduced forage production, grain yield, and visual N deficiency symptoms in no‐till winter wheat (Triticum aestivum L.) prompted this study. Our objectives were to determine the effect of urea placement and two nitrification inhibitors—nitrapyrin [2‐chloro‐6 (trichloromethyl) pyridine] (NP) and dicyandiamide (DCD)—on aerial dry matter and N accumulation. A 4‐yr field study was conducted on a Renfrow silt loam soil (fine‐silty, mixed, thermic Udertic Paleustoli) silt loam near El Reno, OK. The seven treatments included urea fertilizer (60 kg N ha−1) with and without the two inhibitors, surface broadcast or banded 3 to 4 cm below the seed row, and an unfertilized control. Aerial dry matter accumulation during autumn was higher for banded urea plus DCD (22%) and broadcast urea plus DCD (25%), than for broadcast urea without an inhibitor. Whole plant N content during autumn also was higher for banded urea plus DCD (28%) than for broadcast urea without an inhibitor. Neither inhibitor nor placement affected total dry matter accumulation measured at tillering, but differences were noted at spike emergence, gainful, and final harvest. At spike emergence in 1991, when climatic conditions were favorable for early season wheat growth, N content was greater for broadcast urea plus nitrapyrin than for broadcast urea or banded urea without inhibitor. At final harvest, both DCD treatments exhibited greater N content than all other N treatments. In 1993, when dimatic conditions were favorable for leaching, DCD was effective in slowing nitrification and increasing N uptake, regardless of fertilizer placement. Our results suggest that fall application of DCD with urea can potentially increase autumn forage production and N content, thus prolonging the grazing season or accommodating increased stocking rates.

Effects of Surface‐Applied Limestone on the Efficiency of Urea‐Containing Nitrogen Sources for No‐Till Corn

AbstractFertilizer N and lime amendments are commonly surface‐applied to no‐till (NT) production systems, but research on these practices under NT is limited. We examined the effect of surface‐applied limestone on the efficiency of urea, urea‐NH4NO3 (UAN), and NH4NO3 applied broadcast or injected for NT corn (Zea mays L.) production on loessal soils. No‐till field studies were established on two loessal soils in western Tennessee: a Memphis silt loam (fine‐silty, mixed, active, thermic Typic Hapludalf) that had been in NT for 7 yr and a Collins silt (coarse‐silty, mixed, acid, thermic Aquic Udifluvent) that had been under conventional tillage. Corn, with a wheat (Triticum aestivum L.) cover, was established on the Memphis soil in 1990. In 1994, corn was established on the Collins soil. The experimental design was a randomized complete block with a split‐plot arrangement of treatments. Agricultural limestone was surface‐applied at rates of 0 and 1.12 Mg ha−1, 1 to 3 wk before N treatment. The N treatments were UAN broadcast (UAN‐B), UAN injected (UAN‐I), urea broadcast or split‐applied (Urea‐B and Urea‐S), and NH4NO3 broadcast (AN‐B). Nitrogen treatments were applied at 168 kg ha−1 within 5 d after planting. For the split urea treatment, 84 kg ha−1 N was broadcast at planting and 84 kg ha−1 N was surface‐banded at the 8‐leaf growth stage. Applications of AN‐B, UAN‐B, and Urea‐B resulted in lower grain yields and leaf N concentrations than UAN‐I. These reductions were attributed to N immobilization and NH3 volatilization. Average yield reductions attributed to N immobilization were 8% on the Memphis soil and none on the Collins soil. Volatilization losses attributed to UAN‐B were 8 and 12% for the Memphis and Collins soils, respectively. Yield reductions attributed to NH3 volatilization from Urea‐B were 22 and 19% for the Memphis and Collins soils. Splitting the urea application increased yields relative to the Urea‐B treatment only on the Memphis soil. Surface application of limestone decreased Urea‐B yields.

Use of urease inhibitors to reduce ammonia loss from broadcast urea and increase grain yield of flooded rice in Thailand

In Thailand a series of field experiments were run over three years from 1991 to 1993. testing the effects of urease inhibitors on ammonia loss from urea broadcast to flooded rice as well as on grain yield. The results showed that amendment with the algicide terbutryn and the urease inhibitors PPD and NBPT. either alone or in combination significantly reduced NH3 loss and increased grain yield. Experiments with the algicide in combination with the urease inhibitors NBPTO and CHPT demonstrated their effective action in reducing NH3 loss. When used alone urease inhibitors had no effect on grain yield, on the uptake of applied 15N by the grain nor on the uptake of 15N by the whole plant unless an algicide or algicide + nitrification inhibitor was added.

Long Term Effects of Tillage and Nitrogen Source, Rate, and Placement on Grain Sorghum Production

The use of conservation tillage practices has increased substantially in recent years. Few studies have directly compared N management practices and nutrient removal under no-till (NT) and conventional tillage (CT) for grain sorghum [Sorghum bicolor (L.) Moench] over long periods of time. The objective of this study was to determine long-term effects of tillage and N source/placement, and rate on grain sorghum production and composition. A field study was conducted from 1982 to 1992 comparing broadcast ammonium nitrate (BR-AN), broadcast urea ammonium nitrate (BR-UAN), and knifed UAN (KN-UAN), each at 30, 60, and 120 lb N/acre, under NT and CT (chisel-disk) practices. When significant differences in grain yields were observed, they were generally lower for NT than for CT and with BR-UAN than BR-AN. Tillage and N source/placement effects were more evident at the lower N rates. Nitrogen availability, as indicated by flag leaf and grain N concentrations, was higher for CT than for NT and for BR-AN than BR-UAN. The KN-UAN treatments did not have higher grain yields than BR-UAN treatments but did have higher flag leaf and grain N concentrations. There was greater uptake of N in grain under CT than NT. A similar effect was found for P and K uptake by grain but only at the lower N rates. Residue cover, which was measured in 1990 and 1991, was higher for NT than CT but did not increase with increasing N rate under either tillage system. In general, nutrient availability was higher for CT than for NT and N availability was higher for BR-AN and KN-UAN than for BR-UAN. Grain yields were similar across tillage and N source/placement at 120 lb N/acre.